GB899299A - Improvements in or relating to power-assisted liquid pressure braking systems - Google Patents

Abstract

899,299. Fluid-pressure servomotor-control systems. AUTOMOTIVE PRODUCTS CO. Ltd. Aug. 29, 1960 [Sept. 21, 1959]. No.32078/59. Class 135. [Also in Group XXXIV] In a servomotor for a power-assisted fluidpressure braking system (Group XXXIV), a vacuum suspended servomotor 12 is shown in Fig. 1 in conjunction with a tandem master cylinder 15 and the piston 18 of the servomotor 12 has a cavity therein to house a control valve 13, the cavity being divided into two chambers 54 and 55 by a flexible diaphragm 56. On each side of the diaphragm 56, surrounding a hole 57 n its centre, is secured a flanged ring, the two rings 58, 59 together defining a passage connecting the chambers 54 and 55. The working chamber 61 of the servomotor 12 is connected by a passage 62 to the valve chamber 54 and the other chamber 63 in the servomotor is connected by a passage 64 to the valve chamber 55. A rigid partition 65 in the valve cavity divides the valve chamber 54 from a third chamber 66 connected to the atmosphere by means of a flexible conduit 67 extending through the chamber 63. An aperture 68 in the partition 65 connects the chambers 54 and 66, the connection being normally closed in the inoperative position shown by a spring-loaded valve closure disc 69. Depression of the brake pedal 14 causes actuation of the primary producing unit 10 to first of all close the communication between the valve chambers 54 and 55 of the vacuum suspended servo device 12 and further movement causes ring 58 to move the valve closure disc 69 off its seat and allow pressure to be built up in the working chamber 61 of the servomotor via atmosphere connection 67 and open valve device 69 to move servomotor piston 18 to the left and actuate the master cylinder 15. Associated with the primary pressure producing unit 10 is a secondary pressure producing unit 11 comprising a vacuum suspended servomotor 19 having two pistons 21, 22 which are displaced in opposite directions when the servomotor is energized by operation of control valve 27, movement of the pistons 21, 22 causing push rods 25, 26 to actuate master cylinder pistons 35 and 36 associated with the secondary pressure producing unit. The valve 27 which controls the servomotor 19 is divided into three chambers by two flexible diaphragms 92 and 93 and held spaced apart from one another by a cup-shaped member 94 in the chamber 95 between them. The third chamber 98, between the diaphragm 93 and the other end of the casing 91 is provided with a fixed sleeve 99 having an opening 101 which is controlled by a spring-loaded valve closure disc 103. When the system is not in operation the diaphragms 92 and 93 are held by spring 107 in the position shown in Fig. 3 and the valve closure disc 103 is closed. Vacuum normally exists in servomotor chamber 112 through permanent connection 46 and in the condition shown the working chamber 110 of the servomotor 19 is connected to the vacuum reservoir 47 through the conduit 109, chamber 98, orifice 105, orifices 113, chamber 95, passage 111 and servomotor chamber 112. Chamber 96 is connected through conduit 97 to the working chamber 61 of the servomotor 12 and chamber 98 is connected to the working space 110 by conduit 109. When the servomotor 12 is operated, the pressure in the working chamber 61 thereof is transmitted to the chamber 96, the valve 27 and acts on the diaphragm 92 to seat the rim 106 on the valve closure disc 103 to shut off the working chamber 110 and the servomotor 19 from the vacuum reservoir 47. Further movement of the member 94 lifts the valve closure disc 103 to admit atmospheric air to the working chamber 110 of the servomotor 19 and build up a pressure in the valve chamber 98 opposing that in the chamber 96 which tends to reseat the valve closure disc 103 on the rim 102 when it reaches a predetermined value. When the air pressure in the working chamber 61 of the servomotor 12 reaches a predetermined value, the valve 27 is operated to bring the servomotor 19 into action, moving the pistons 21, 22 of that servomotor to cause the push rods 25, 26 to close the passages in the pistons 35 and 36 of the master cylinders 23, 24 and build up pressure in those master cylinders to increase the pressure acting on the brake motor cylinders 45. As the area of the pistons 21, 22 and the servomotor 19 is greater in relation to the area of the pistons 35, 36, the master cylinders 23, 24 than is the area of the piston 18 of the servomotor 12 in relation to the area of the piston 16, 28 of the tandem master cylinder, a considerably greater pressure can be produced by the secondary pressure producing unit than by the primary pressure producing unit and, since the operation of the primary unit has already taken up shoe clearance only a small quantity of liquid has to be displaced by the secondary unit. Should the servomotor 12 fail, the piston 18 can be moved directly by the pedal 14 to actuate the master cylinder 15.